R无法解析

问题：

I just downloaded and installed the new Android SDK. 我刚刚下载并安装了新的Android SDK。 I wanted to create a simple application to test drive it. 我想创建一个简单的应用程序来测试驱动器。

The wizard created this code: 向导创建了以下代码：

1package eu.mauriziopz.gps;
2
3import android.app.Activity;
4import android.os.Bundle;
5
6public class ggps extends Activity {
7    /** Called when the activity is first created. */
8    @Override
9    public void onCreate(Bundle savedInstanceState) {
10        super.onCreate(savedInstanceState);
11        setContentView(R.layout.main);
12    }
13}

but Eclipse gives me the error 但是Eclipse给了我错误

R cannot be resolved R无法解析

on line 在线

setContentView(R.layout.main);

Why? 为什么？

PS: I do have an XML file named main.xml under res/layout/ . PS：我确实在res/layout/下有一个名为main.xml的XML文件。

解决方案：

参考一： https://stackoom.com/question/3iEL/R无法解析-Android错误
参考二： https://oldbug.net/q/3iEL/R-cannot-be-resolved-Android-error